SmartGit/Hg is a graphical user interface for Git and Mercurial which can work with SVN
repositories.
It supports cloning from common repository providers (e.g.,
GitHub,
Assembla),
assists Git newbies,
and also offers the advanced, powerful Git features.
It provides several tools to help create clean commits, for example by
allowing the user to commit just parts of changes files and reordering
and squashing unpushed commits.
If you are using GitHub or GitHub Enterprise,
SmartGit/Hg can work easily with pull
requests (creation,
resolving) and commit comments.
SmartGit/Hg ships with a built-in SSH client,
file comparer, and merge tool which are capable
of syntax coloring for many languages.

Atlassian Stash delivers a central, secure solution for creating and managing distributed Git repositories on your own servers. It has an easy-to-use interface for adding users and groups and creating and managing repositories, and a Project Structure for logically grouping your repositories. Installed on your own network, administrators have full control over how Stash fits into their environment. It supports Atlassian’s plugin framework plus a full, open REST API for customized integrations. Key features include simple administration, easy permissions around Git repositories, LDAP (Active Directory) integration, JIRA issue tracker integration, cloning, and more.

Tada is a Git client that handles multiple Git repositories simultaneously. Its user interface is based on consoloid technology, so it can be controlled with words in addition to the mouse pointer. It works on the desktop as well as on mobile devices.

PHP Git Client Class is a class for accessing files in Git repositories. It can connect to a remote repository and checkout files similar to the git clone command, and retrieve the log of changes to a file.